DENGUE HAEMORRHAGIC FEVER IN LORONG LEW LIAN (Causes)

[Mr Deputy Speaker in the Chair]

Mr Goh Choon Kang asked the Minister for the Environment what were the causes of the recent outbreak of dengue fever and dengue haemorrhagic fever in Lorong Lew Lian.

Dr Ahmad Mattar: Mr Deputy Speaker, Sir, Dengue Fever/Dengue Haemorrhagic Fever (DF/DHF) is a mosquito-borne disease which is endemic in Singapore. Disease transmission occurs throughout the year as the dengue virus and the Aedes mosquitoes carrying the virus are are both present in the country. Outbreaks can occur if there is an increase in the virulence of the dengue virus or an increase in the Aedes mosquitoes in a human population which is highly susceptible to the disease.

There is a comprehensive island-wide Aedes mosquito prevention and control programme implemented by the Environment Ministry. The strategies are based on an integrated approach incorporating source reduction, health education and law enforcement. The overall Aedes population as measured by the Aedes House Index (which is the percentage of houses positive for Aedes mosquitoes) has been drastically reduced from more than 25% in 1969 to 1.1% in 1986.

In spite of the reduction in Aedes population, outbreaks occur once in every few years. The notable outbreaks occurred in 1973 with 1,187 cases, 27 deaths; 1978 with 384 cases, 2 deaths; 1986 with 354 cases, one death and todate (this year) 302 cases, 2 deaths. In between these years, the average number of cases is 144 with one or two deaths a year.

The Ministry of the Environment is concerned with the periodic outbreaks of DF/DHF and has demarcated 42 dengue "sensitive" areas for priority Aedes control. These areas are identified based on the distribution of past cases of DF/DHF, Aedes breeding habitats, human population density, housing types and development activities. They are closely monitored for any build-up of Aedes mosquito population.

As there is no vaccine against DF/DHF, the only means to minimize periodic outbreaks is to ensure that the Aedes population is maintained at a very low level throughout the country. This could be achieved if the members of the public play a greater role in preventing Aedes mosquito breeding both within and outside their premises. They should avoid keeping stagnant water and ensure that all water storage containers are tightly covered to prevent mosquitoes from laying eggs.

On the outbreak at Lorong Lew Lian, routine surveys revealed that the Aedes House Index was about 2%. Aedes breeding was found in the uncompleted HDB blocks of flats at the proposed Serangoon South Estate, roof-top water tanks at Lorong Lew Lian, and ornamental containers in residential premises. As soon as a cluster of three cases was identified in Lorong Lew Lian on 28 October, epidemic vector control measures were immediately implemented. Up to 23 November 1987, a total of 7,043 premises have been inspected, 4,499 fogged with insecticides and 3,067 health education pamphlets distributed. The outbreak is being brought under control. As at 28 November, a total of 48 cases have been reported.

The Ministry of the Environment will continue to educate the public on the prevention of Aedes mosquitoes breeding and to monitor the Aedes population and the disease situation closely.

Mr Chiam See Tong: Sir, how many prosecutions were made by the Ministry for the year ending 31st December last year?

Dr Ahmad Mattar: Sir, the Member for Potong Pasir is fond of asking for figures. I do not have the figures. If he likes he can file a question for Oral Answer.

Dr Ang Kok Peng: Sir, I believe there are regulations under the Destruction of Disease-Bearing Insects Act which require building contractors to take adequate measures to prevent the breeding of mosquitoes at construction sites. May I ask the Minister whether these regulations are being strictly enforced, and what are the penalties for contractors who contravene these regulations?

Dr Ahmad Mattar: Sir, all construction sites are inspected by officers of my Ministry on a monthly basis. Under the Destruction of Disease-Bearing Insects Act (DDBIA), any person who refuses, fails, or neglects to comply with the Order served upon him by the Commissioner of Public Health shall be liable, upon conviction, to a fine not exceeding $1,000 or to imprisonment not exceeding three months or to both, and to a further fine of not more than $100 for every day during which the offence continues after conviction. In addition, Sir, the Commissioner of Public Health may enter the worksite, carry out remedial measures and recover all costs and expenses from the contractor concerned.

Mr Ng Kah Ting: Sir, can I ask the Hon. Minister what are the measures his Ministry will take with a view to totally eradicating this Aedes mosquito menace. And if these measures are not possible to totally eradicate such a menace, what other steps does his Ministry propose to take to reduce the mosquito population?

Dr Ahmad Mattar: Mr Deputy Speaker, Sir, I share the concern of the Member for Punggol but I am afraid I have got to disappoint him. It is not possible for us to eradicate Aedes mosquitoes in Singapore because we are living in a region where Aedes mosquito breeding is a problem. But my Ministry has identified three areas where Aedes breeding can still pose a problem to us.

The first problem area, Sir, is the construction sites. My Ministry will now require all major construction sites to engage pest control firms to undertake pest control work for them. The contractor concerned must ensure that the pest control firm he engages is capable of carrying out vector control work effectively. The contractor may be required to submit details of the work carried out by the pest control firms e.g. the number of inspections made, the oiling, fogging, etc.

The second problem area, Sir, is the roof-top water tanks in HDB estates. Profuse Aedes mosquito breedings have been found in roof-top water tanks in many of these estates. The HDB has consulted my Ministry on the design of new roof-top water tanks which will be mosquito-free. These new water tanks are being installed now. In the meantime, the older water tanks are being repaired to make sure that mosquito cannot breed in them.

The third area, Sir, is breeding of Aedes mosquitoes in the homes. Home occupiers who keep pots of plants must make sure that the plates they normally put beneath the pots do not contain stagnant water. Better still, if they could do away with these plates. Home occupiers must also pay heed to other receptacles lying about which may collect water. These receptacles should be removed or placed in such a way that the water cannot collect in them. In this regard, Sir, my Ministry will intensify its public health education programme.

Dr Aline K. Wong (Changkat): Sir, I would like to ask the Minister for the Environment that if it is impossible to eradicate dengue fever, how was it possible that malaria was eradicated and what were the differences involved?

Dr Ahmad Mattar: Sir, I think the Member for Changkat is under the impression that we have eradicated malaria completely. No. We do have malaria cases imported into Singapore. As I have said, even if we eradicate Aedes mosquito breeding in Singapore, there are still carriers of Aedes mosquitoes, since we are living in a region where Aedes mosquito breeding is a problem.